Been making my own seltzer for quite some time. Easy enough to add simple syrup and flavorings.
Do a web search and you can find all the hardware you’ll need, from coldplates to stainless valves and high pressure hoses, to make your own system for a very fair price.
Much less than a McCann carbonator and other required components.
Sodastream is really quite lame, and not cheap.
Not enough bubbles and goes flat right away.
Some basic plumbing hardware and a CO2 canister and your good to go.
As someone who enjoyed fountain “RC” cola from Bob’s Lunch & Fountain back in the day, I really groove on maximum bubbles.
I bought a sodastream years ago and gave it to the grandkids for the reasons you stated. Just wasn’t carbonated enough and even if you could get it carbonated it fell flat almost immediately. Plus the mixes tasted like crap to me.
Bleh!